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* Support Sync Batch Norm.
* Note, do not enable it in one device.

Usage:

build_strategy = fluid.BuildStrategy()
build_strategy.sync_batch_norm = True
binary = fluid.compiler.CompiledProgram(tp).with_data_parallel(
        loss_name=loss_mean.name,
        build_strategy=build_strategy)

* Impl fp16 compute kernel for slice_op

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* Use data() to replace mutable_data()

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2. remove lod check in reshape op
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* Add cpu_quantize_squash_pass for C-API quantization

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* add cpu_quantize_squash_pass teste

* fix lint: add include memory unorderd_map and unordered_set

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* lint fix 2

* fixes

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* refactored

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* fix windows ci

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* resolve #15618
Backgroud: the PR #15398 raised the box_coder op performance regression, we optimized the code via the more efficency leveraging opemmp.

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* fix broadcast with mp mode

* polish code test=develop

* fix bcast strategy test=develop

* fic cpplint test=develop

* fix py3 failed test=develop

* fix comment test=develop

* update comment test=develop

* remove concast_cast and refactor code test=develop

* reduce flag use test=develop

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* Remove Desc in Forward Pass

* Refactor VarBase

* Add dbg info

* Only check type in imperative mode

* Polish code and support optimizer

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* Fix stop gradient problem in PyLayer

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* Revert "Revert "Add Event for TensorCopy" (#16022)"

This reverts commit e2da3a5b.

* use default stream
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* fix recordio on win
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* test=develop

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* fix code style
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* test=develop

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* fix deadlink

fix https://github.com/PaddlePaddle/FluidDoc/issues/679

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* test=develop